The invention relates to a device for varying the control times of gas exchange valves of an internal combustion engine and is particularly advantageously implementable on hydraulic camshaft adjusting devices in a rotary piston design.
Such a device was generically disclosed by EP 0 818 610 A2. This device, configured as what is known as a vane cell adjusting device, comprises first a drive wheel configured as an outer rotor and drive-connected to a crankshaft of the internal combustion engine, which drive wheel comprises a cavity formed by a hollow cylindrical peripheral wall and two lateral walls. Within this cavity five hydraulic working spaces are formed by five delimitation walls starting from the inside of the peripheral wall and oriented toward the longitudinal central axis of the drive wheel. The device further comprises an impeller wheel configured as an inner rotor, connected in a rotationally fixed manner to a camshaft of the internal combustion engine and inset into the cavity of the drive wheel. On the periphery of its wheel hub, the impeller wheel in turn has five blades, each disposed in an axial retaining groove, which each extend radially into a hydraulic working space of the drive wheel and divide the latter into pairs of hydraulic pressure chambers working in opposition to one another. Each blade of the impeller wheel is pressed radially, by the force of a spring element on its lower end surface in the axial retaining groove, by its upper end surface against the inside of the peripheral wall of the drive wheel. As a result, the pressure chambers of each hydraulic working space are sealed off from one another and, when selectively or simultaneously subjected to the action of pressure by means of a hydraulic pressure medium, effect a pivot movement or fixing of the impeller wheel relative to the drive wheel and hence of the camshaft relative to the crankshaft.
It is a disadvantage of this known device that when one or both pressure chamber(s) of each hydraulic working space are subjected to the action of pressure, a pressure build-up also takes place in the sealing gap between the upper end surface of each blade and the inside of the peripheral wall of the drive wheel. If the compressive force here exceeds the value of the spring force of the spring element disposed at the lower end surface of each blade, then, despite these spring elements, what is known as xe2x80x9cblade dippingxe2x80x9d may occur, meaning a radial displacement of the blades against the force of their spring elements. This in turn causes increased pressure medium leakages between the individual pressure chambers of the hydraulic working spaces, so that inferior hydraulic tensioning of the impeller wheel relative to the drive wheel occurs. In addition, these increased pressure medium leakages can be the cause of major deviations from the predetermined angle of adjustment between camshaft and crankshaft and of longer periods for the adjustment of the device.
It is therefore an object of the invention to design a device for varying the control times of gas exchange valves of an internal combustion engine, especially a hydraulic camshaft adjusting device in a rotary piston design, in which the radial displacement of the blades against the force of their spring elements arising from the pressure build-up in the sealing gap between the upper end surface of each blade of the impeller wheel and the inside of the peripheral wall of the drive wheel is effectively prevented.
according to the invention, this object is achieved with a device in accordance with the present invention, in that when one or both pressure chamber(s) of each hydraulic working space of the device are subjected to the action of pressure, each blade of the impeller wheel, in addition to the force of its spring element, can be pressed radially by the compressive force of the hydraulic pressure medium that can be selectively applied to its lower end surface, by its upper end surface against the inside of the peripheral wall of the drive wheel.
In an expedient further development of the invention, the entire lower end surface of each blade of the impeller wheel is simultaneously configured as its pressure impact surface, acting in the radial direction to the peripheral wall of the drive wheel, for the hydraulic pressure medium. In addition, each blade comprises, on one or both of its lateral surface(s), at least one additional pressure-medium channel starting from its lower end surface, which is directly or indirectly hydraulically connected to at least one of the pressure chambers adjoining the respective blade.
In a further embodiment of the invention, this additional pressure-medium channel on one or both lateral surface(s) of each blade is, depending on the embodiment, preferably disposed on or close to the longitudinal central axis of each blade, in order to achieve a uniform pressure build-up at its pressure impact surface and prevent axial tilting of the blade in its retaining groove. The direct or indirect hydraulic connection to at least one of the pressure chambers of the device adjoining the respective blade is, by contrast, achieved by a variable length of the additional pressure-medium channel, in that the latter optionally ends above or below or precisely at the height of the peripheral surface of the wheel hub of the impeller wheel. As a result, the pressure-medium pressure acting on the pressure impact surface of the blade can be set so that, with decreasing length of the additional pressure-medium channel toward the pressure impact surface of the blade, the pressure-medium pressure building up at the pressure impact surface can be reduced. This means that, with an additional pressure-medium channel of a length ending above or precisely at the height of the peripheral surface of the wheel hub of the impeller wheel, the pressure-medium pressure in the pressure chamber directly connected to the pressure-medium channel also prevails at the pressure impact surface of the blade. However, the further the additional pressure-medium channel ends below the height of the peripheral surface of the wheel hub of the impeller wheel, the lower becomes the pressure-medium pressure at the pressure impact surface of the blade, throttled by the gap between the lateral surface of the blade and the groove wall of the retaining groove of the blade.
In a particularly advantageous first embodiment of the additional pressure-medium channel on one or both lateral surfaces of each blade, the latter is preferably configured as a radial groove machined into the lower end surface of the blade and continuous from one lateral surface to the other lateral surface of the blade. This radial groove has a length ending below the peripheral surface of the wheel hub of the impeller wheel and is thus indirectly hydraulically connected to both of the pressure chambers of the device adjoining the blade. In addition, the radial groove preferably has a width approximately corresponding to the thickness of the blade and is directly machined into the blade along the longitudinal central axis thereof. However, the width of the radial groove and/or its arrangement relative to the longitudinal central axis of the blade may also be variably configured. The pressure medium leakages possible with an additional pressure-medium channel configured in this way between the two pressure chambers of the device adjoining each blade are prevented, at least when only one pressure chamber of each of the hydraulic working spaces is subjected to the action of pressure, in that the blades, as a result of the unilateral action of pressure, perform a slight tilting movement within their axial retaining grooves toward whichever chamber is not subjected to the action of pressure. As a result of the linear contact between their lateral surfaces limiting the pressure chambers not subject to the action of pressure and the edge at which their axial retaining grooves make the transition to the peripheral surface to the wheel hub of the impeller wheel, the blades then automatically form a gap seal relative to the pressure chambers not subjected to the action of pressure, whereby the passage of the hydraulic pressure medium from one pressure chamber to the other is prevented. It is also possible, however, to configure the additional pressure-medium channel on each blade, configured as a radial groove, with a length ending precisely on or above the peripheral surface of the wheel hub of the impeller wheel and thus to connect it hydraulically to both pressure chambers of the device adjoining each blade. As a result, the pressure build-up on the pressure impact surface of the blade can advantageously be accelerated, but the increased pressure medium leakages thereby arising between the two pressure chambers and the reduced pressure-medium pressure resulting must be taken into account.
In an equally advantageous second embodiment of the additional pressure-medium channel on one or both lateral surfaces of each blade, the latter is preferably configured as two part-channels each machined into a lateral surface of the blade and formed as a radial indentation or basic groove in the blade. Each of these part-channels also has a length preferably ending below the peripheral surface of the wheel hub of the impeller wheel and is thus indirectly hydraulically connected to both of the pressure chambers of the device adjoining the blade. In addition, the part-channels, as in the first embodiment of the additional pressure-medium channel, preferably have a width approximately corresponding to the thickness of the blade us are machined, to a depth corresponding to approximately one third of the thickness of the blade, into the lateral surfaces of the blade along the longitudinal central axis thereof. Instead of a part-channel in each lateral surface of the blade having such a width, however, it is also possible to divide each part-channel into two or more narrower channel arms, which are disposed parallel to one another and symmetrically relative to the longitudinal central axis of the blade on each lateral surface of the blade. Similarly, for example if the disadvantageous radial displacement of the blades on the impeller wheel is to be prevented only if one pressure chamber of the device is subjected to the action of pressure, it may be of advantage to machine one or several of these part-channels or channel arms into only one lateral surface of each blade. Irrespective thereof, the pressure medium leakages possible with such an additional pressure-medium channel between the two pressure chambers of the device adjoining each blade are again prevented, as in the first embodiment, as a result of the linear contact arising in the event of a unilateral action of pressure between the lateral surfaces of the blades and the edge at which their axial retaining grooves make the transition to the peripheral surface to the wheel hub of the impeller wheel. In addition, in this embodiment also, for accelerated build-up of pressure at the pressure impact surface of each blade, it is possible to configure the additional pressure-medium channel, subdivided into part-channels or alternatively into channel arms and having a length ending precisely on or above the peripheral surface of the wheel hub of the impeller wheel and thus to connect it hydraulically directly to both pressure chambers of the device adjoining each blade, though here again the increased pressure medium leakages between the two pressure chambers must be taken into account.
The device configured according to the invention for varying the control times of gas exchange valves of an internal combustion engine, especially a hydraulic camshaft adjusting device in a rotary piston design, thus comprises, by comparison with the devices known from the prior art, the advantage that when one or both pressure chamber(s) of each hydraulic working space of the device are subjected to the action of pressure, what is known as xe2x80x9cblade dippingxe2x80x9d, in other words the radial displacement of the blades against the force of their spring elements resulting from the pressure build-up in the sealing gap between the upper end surface of each blade of the impeller wheel and the inside of the peripheral wall of the drive wheel is effectively prevented. This is achieved, according to the invention, by the selective application of the compressive force of the hydraulic pressure medium to the lower end surface, configured as a pressure impact surface, of each blade, so that in addition to the force of their spring elements the blades can be pressed radially by their upper end surfaces against the inside of the peripheral wall of the drive wheel. As this merely requires an additional pressure-medium channel on one or both lateral surface(s) of each blade, starting from its lower end surface, cost-effective production of the device configured according to the invention may be claimed as a further advantage thereof.